By HERBERT SPENCER. New and revised (sixth) edition of the first volume of the author's Synthetic Philosophy. This fundamental and most important work has been changed in substance and in form to a considerable extent, and largely rewritten and wholly reset. It is now forty years since the author began the "First Principles," and its presentation in this definitive form, with the author's last revisions, is an event of peculiar interest and consequence. While experience has not caused him to recede from the general principles set forth, he has made some important changes in the substance and form. His amendments of matter and manner are now final. The contents of the several volumes of the series are as follows: 1. First Principles. I. The Unknowable. II. The Knowable. 2. The Principles of Biology. Vol. 1. I. The Data of Biology. II. The Inductions of Biology. III. The Evolution of Life. 3. The Principles of Biology. Vol. 2. IV. Morphological Development. V. Physiological Development. VI. Laws of Multiplication. 4. The Principles of Psychology. Vol. 1. I. The Data of Psychology. II. The Inductions of Psychology. III. General Synthesis. IV. Special Synthesis. V. Physical Synthesis. 5. The Principles of Psychology. Vol. 2. VI. Special Analysis. VII. General Analysis. VIII. Congruities. IX. Corollaries. 6. The Principles of Sociology. Vol. 1. I. The Data of Sociology. II. The Inductions of Sociology. III. The Domestic Relations. 7. The Principles of Sociology. Vol. 2. IV. Ceremonial Institutions. V. Political Institutions. 8. The Principles of Sociology. Vol. 3. VI. Ecclesiastical Institutions. VII. Professional Institutions. VIII. Industrial Institutions. 9. The Principles of Ethics. Vol. 1. I. The Data of Ethics. II. The Inductions of Ethics. III. The Ethics of Individual Life. 10. The Principles of Ethics. Vol. 2. IV. The Ethics of Social Life: Justice. V. The Ethics of Social Life: Negative Beneficence. VI. The Ethics of Social Life: Positive Beneficence. D. APPLETON AND COMPANY, NEW YORK. * * * * * BOOKS BY PROF. G. FREDERICK WRIGHT. THE SCIENTIFIC ASPECTS OF CHRISTIAN EVIDENCES. By G. FREDERICK WRIGHT, D.D., LL.D., F.G.S.A., Professor of the Harmony of Science and Revelation, Oberlin College; Author of "The Logic of Christian Evidences," "The Ice Age in North America," etc. Illustrated. 12mo. Cloth, $1.50.